The present invention relates to a method of increasing the volume of moist tobacco. More particularly, the invention relates to improvements in a method of increasing the volume of tobacco leaves or portions of leaves by subjecting such tobacco particles to the action of a high-frequency field which causes a vaporization of moisture in capillaries of tobacco particles with attendant expansion of capillaries and the resulting increase in volume of tobacco.
The minimum weight of cigarettes or analogous tobacco-containing articles is usually prescribed by law. Since the manufacturers try to maintain the weight of tobacco in a smokers' product as close to the minimum permissible weight as possible, and since the mass of such minimum quantity of tobacco is often insufficient to properly fill the wrapper of a cigarette or a like smokers' product, the manufacturers strive to expand (i.e., to increase the volume of) tobacco particles in order to make sure that a quantity of tobacco having the minimum permissible weight will produce an article having the desirable "feel" or firmness in the hand of a smoker and that particles of tobacco will be less likely to escape at the ends of rod-like tobacco fillers in cigarettes or the like. It is a well known fact that tobacco particles are more likely to escape at the ends of relatively soft cigarettes wherein the tendency of tobacco particles to shift is much more pronounced than in a relatively tightly packed cigarette.
German Pat. No. 738,726 discloses a method of increasing the volume of tobacco particles by subjecting such particles to the action of a high-frequency electric field, especially a field of ultrashort waves with an output of 4-5 watts per gram of tobacco. The high-frequency field causes vaporization of water in the capillaries of tobacco with attendant expansion, and the tobacco is thereupon immediately cooled. The reason for expansion of tobacco in a high-frequency field is that the temperature of water in capillaries (and hence the pressure of resulting steam rises too rapidly to allow for complete diffusion of steam through the walls of the capillaries. Thus, the rising steam pressure causes a desirable expansion of capillaries; such procedure is known as "puffing".
The immediate cooling of freshly expanded tobacco is considered necessary in order to avoid excessive losses in mositure content. The cooling action is sufficiently intensive to bring about a condensation of steam in the capillaries. It was found that the just described conventional treatment causes undesirable bursting of capillaries so that the expanded and cooled tobacco yields a relatively high percentage of tobacco dust. The bursting capillaries release the steam so that the latter can escape and thus allows for substantial contraction or shrinkage of tobacco. As a result of frequent bursting of capillaries, escape of steam and ensuing shrinkage, the maximum increase in volume of tobacco which is treated in accordance with the method of the aforementioned German patent is only in the range of about 20 percent. In other words, the increase in volume is far from satisfactory, especially when compared with the outlay for machinery and energy which must be utilized to first subject tobacco to the action of a high-frequency field and to thereupon immediately cool freshly expanded tobacco in order to avoid an excessive reduction in moisture content.